Dans le domaine du développement d'outils de micromanipulation de haute précision pour le biomédical, les microrobots mobiles immergés font figures de technologie émergente prometteuse pour des applications in-vitro, puis à plus long terme pour l'in-vivo. Mes travaux portent sur l'étude de la propulsion de microrobots par voie magnétique dans des fluides circulant dans des microcanaux, à une échelle où les phénomènes d'adhérence et d'amortissement prévalent. Leur application pour des opérations de transduction est développée dans un deuxième volet.Un dispositif d'asservissement par vision à haute fréquence d’échantillonnage (~5kHz) a été développé rendant possible le contrôle sous champ magnétique uniforme ou gradient. Les performances du système ont notamment demandé l’implémentation d'une interface multi-tâches afin de pouvoir acquérir et traiter les images en parallèle de l'actuation du robot. L'analyse de la dynamique permet de mieux appréhender les phénomènes parfois imprévisibles liés au déplacement du robot, MagPol, intégré dans une puce microfluidique. Il peut réciproquement servir de capteur dans son environnement fluidique.Ce design original de robot a été conçu pour la micromanipulation et permet également d'explorer des nouvelles stratégies de déplacement. Ces capacités ont été éprouvées sur des objets de même taille qu'en biologie cellulaire (billes, bulles).Enfin, une démonstration de l'asservissement visuel en planification de tâche a été effectuée. Sous réserve de posséder un algorithme suffisamment performant, l'échantillonnage haute fréquence en temps réel devient possible et l'observation de performances sur des trajectoires complexes est démontrée. Les performances, la portabilité et la reproductibilité du système démontrent des capacités de transduction à haut débit qui sont très prometteuses pour l'aspect applicatif. / In the research for new high performances tool for micrometric scale manipulation, mobile microrobots immersed are considered as a promising technology for in-vitro applications, and with a long term view in-vivo. My work focuses on the propulsion study of mobile microrobots immersed in microfluidic channels controlled through electromagnets. At this scale, surface and damping phenomena predominates. Application for transduction operation is developed in a second part.A high sampling rate (≈5kHz) visual servoing setup have been developed making a control possible through uniform and gradient magnetic field. Performances of the system have notably required a multi-thread programmed user interface to acquire and analyze the frame in parallel of the robot actuation. Dynamic analysis allow to better apprehend the perturbation dynamics of the robot MagPol, integrated in a microfluidic chip. It can reciprocally serve as a sensor for in fluidic environment.MagPol design has been originally conceived for micromanipulation, and also allows to explore new displacement strategies. Its capacities have been tested on beads and bubbles equivalent to cell biology characteristic size (10µm – 100µm).Finally, a demonstration of planned trajectory using visual servoing was accomplished. Though it has required an algorithm sufficiently efficient, high frequency real-time sampling is possible and lead to control and post observation on complex trajectory. Global performances, repeatability and portability of our system has demonstrated its capacities as a high-throughput transducer, promising for single microagent applications.

Micro Autonomous Systems and Technologies (MAST) is an Army Research Laboratory (ARL) sponsored project based on a consortium of revolutionary academic and industrial research institutions working together to develop new technologies in the field of microelectronics, autonomy, micromechanics and integration. The overarching goal of the MAST consortium is to develop autonomous, multifunctional, and collaborative ensembles of microsystems to enhance small unit tactical situational awareness in urban and complex terrain. Unmanned systems are used to obtain intelligence at the macro level, but there is no real-time intelligence asset at the squad level. MAST seeks to provide that asset. Consequently, multiple integrated MAST heterogeneous platforms (e.g. crawlers, flyers, etc.) working together synergistically as an ensemble shall be capable of autonomously performing a wide spectrum of operational functions based on the latest developments in micro-mechanics, micro-electronics, and power technologies to achieve the desired operational objectives. The design of such vehicles is, by nature, highly constrained in terms of size, weight and power. Technologists are trying to understand the impacts of developing state-of-the-art technologies on the MAST systems while the operators are trying to define strategies and tactics on how to use these systems. These two different perspectives create an integration gap. The operators understand the capabilities needed on the field of deployment but not necessarily the technologies, while the technologists understand the physics of the technologies but not necessarily how they will be deployed, utilized, and operated during a mission. This not only results in a major requirements disconnect, representing the difference of perspectives between soldiers and the researchers, but also demonstrates the lack of quantified means to assess the technology gap in terms of mission requirements. This necessitates the quantification and resolution of the requirements disconnect and technology gap leading to re-definitions of the requirements based on mission scenarios. A research plan, built on a technical approach based on the simultaneous application of decomposition and re-composition or 'Top-down' and 'Bottom-up' approaches, was used for development of a structured and traceable methodology. The developed methodology is implemented through an integrated framework consisting of various decision-making tools, modeling and simulation, and experimental data farming and validation. The major obstacles in the development of the presented framework stemmed from the fact that all MAST technologies are revolutionary in nature, with no available historical data, sizing and synthesis codes or reliable physics-based models. The inherently multidisciplinary, multi-objective and uncertain nature of MAST technologies makes it very difficult to map mission level objectives to measurable engineering metrics. It involves the optimization of multiple disciplines such as Aero, CS/CE, ME, EE, Biology, etc., and of multiple objectives such as mission performance, tactics, vehicle attributes, etc. Furthermore, the concept space is enormous with hundreds of billions of alternatives, and largely includes future technologies with low Technology Readiness Level (TRL) resulting in high uncertainty. The presented framework is a cyber-physical design and analysis suite that combines Warfighter mission needs and expert technologist knowledge with a set of design and optimization tools, models, and experiments in order to provide a quantitative measure of the requirements disconnect and technology gap mentioned above. This quantification provides the basis for re-definitions of the requirements that are realistic in nature and ensure mission success. The research presents the development of this methodology and framework to address the core research objectives. The developed framework was then implemented on two mission scenarios that are of interest to the MAST consortium and Army Research Laboratory, namely, Joppa Urban Dwelling and Black Hawk Down Interior Building Reconnaissance. Results demonstrate the framework’s validity and serve as proof of concept for bridging the requirements disconnect between the Warfighter and the technologists. Billions of alternative MAST vehicles, composed of current and future technologies, were modeled and simulated, as part of a swarm, to evaluate their mission performance. In-depth analyses of the experiments, conducted as part of the research, presents quantitative technology gaps that needs to be addressed by technologist for successful mission completion. Quantitative values for vehicle specifications and systems' Measures of Performance were determined for acceptable level of performance for the given missions. The consolidated results were used for defining mission based requirements of MAST systems.

The development of synthetic life once envisioned by Feynman and Flynn many decades ago has stimulated significant research in materials science, biology, neuroscience, robotics, and computer science. The cross-disciplinary effort and advanced technologies in soft miniature robotics have addressed some of the significant challenges of actuation, sensing, and subsystem integration. An ideal Soft motile miniaturised robot (SMMRs) has innovative applications on a small scale, for instance, drug delivery to environmental remediation. Such a system demands smart integration of micro/nano components such as engines, actuators, sensors, controllers, and power supplies, making it possible to implement complex missions controlled wirelessly. Such an autonomous SMMR spans over multiple science and technology disciplines and requires innovative microsystem design and materials. Over the past decade, tremendous efforts have been made towards mastering one of such a SMMR's essential components: micro-engine. Chemical fuels and magnetic fields have been employed to power the micro-engines. However, it was realized seven years ago in work of TU-Chemnitz Professorship of Material Systems in Nanoelectronics and institute of investigative Nanosciences Leibniz IFW Dresden including Chemnitz side. Write explicitly that it is essential to combine the micro-engine with other functional microelectronic components to create an individually addressable smart and motile microsystem. This PhD work summarises the progress in designing and developing a novel flexible and motile soft micro autonomous robotic tubular systems (SMARTS) different from the well-studied single-tube catalytic micro-engines and other reported micromotors. Our systems incorporate polymeric nanomembranes fabricated by photolithography and rolled-up nanotechnology, which provide twin-tube structures and a spacious platform between the engines used to integrate onboard electronics. Energy can be wirelessly transferred to the catalytic tubular engine, allowing control over the SMARTS direction. Furthermore, to have more functionality onboard, a micro-robotic arm was integrated with remote triggering ability by inductive heating. To make the entire system smart, it is necessary to develop an onboard processor. However, the use of conventional Si technology is technically challenging due to the high thermal processes. We developed complex integrated circuits (IC) using novel single crystal-like organic and ZnO-based transistors to overcome this issue. Furthermore, a novel fabrication methodology that combines with six primary components of an autonomous system, namely motion, structure, onboard energy, processor, actuators, and sensors to developing novel SMARTSs, is being pursued and discussed.:List of acronyms 8 Chapter 1. Introduction 12 1.1 Motivation 14 1.2 Objectives 17 1.3 Thesis structure 18 Chapter 2. Building blocks of micro synthetic life 19 2.1 Soft structure 20 2.1.1 Polymorphic adaptability 20 2.1.2 Dynamic reconfigurability 20 2.1.3 Continuous motion 21 2.2 Locomotion 21 2.2.1 Aquatic 22 2.2.2 State-of-the-art aquatic SMMR 24 2.2.3 State-of-the-art terrestrial SMMR 25 2.2.4 State-of-the-art aerial SMMR 27 2.3 Onboard sensing 28 2.3.1 State-of-the-art 3D and flexible sensors systems 28 2.4 Onboard actuation 30 2.4.1 State-of-the-art actuators 30 2.5 Embedded onboard intelligence 32 2.5.1 State-of-the-art flexible integrated circuits 32 2.6 Onboard energy 33 2.6.1 State-of-the-art micro energy storage 34 2.6.2 State-of-the-art onboard energy harvesting SMMR 35 Chapter 3. Technology overview 38 3.1 Structure 38 3.1.1 Self-assembled “swiss-roll” architectures 40 3.1.2 Polymeric “swiss-roll” architectures 41 3.2 Motion: micro tubes as propulsion engines 44 3.2.1 Chemical engines 44 3.3 Embedded onboard intelligence 46 3.3.1 Thin film transistor 46 3.3.2 Basic characteristics of MOSFETs 48 3.4 Growth dynamics of organic single crystal films 51 3.4.1 Thin films growth dynamics 52 3.5 Powering SMARTSs 55 3.5.1 Onboard energy storage 56 3.5.2 Wireless power delivery 59 3.6 Integrable micro-arm 63 3.6.1 Stimuli-responsive actuator 63 3.6.2 Remote activation 64 Chapter 4. Fabrication and characterization 65 4.1 Thin film fabrication technology 65 4.1.1 Photolithography 65 4.1.2 E-beam deposition 68 4.1.3 Sputtering 69 4.1.4 Physical vapour deposition 70 4.1.5 Atomic layer deposition 71 4.1.6 Ion beam etching 72 4.2 Characterization methods 73 4.2.1 Atomic force microscopy 73 4.2.2 Scanning electron microscopy 74 4.2.3 Cyclic voltammetry 75 4.2.4 Galvanic charge discharge 77 4.2.5 Electrochemical impedance spectroscopy 78 Chapter 5. Development of soft micro autonomous robotic tubular systems (SMARTS) 81 5.1 Soft, flexible and robust polymeric platform 82 5.2 Locomotion of SMARTS 84 5.2.1 Assembly of polymeric tubular jet engines 84 5.2.2 Catalytic self-propulsion of soft motile microsystem 85 5.2.3 Propulsion power generated by the catalyst reaction 87 5.3 Onboard energy for SMARTS 89 5.3.1 Onboard wireless energy 90 5.3.2 Onboard ‘zero-pitch’ micro receiver coil 90 5.3.3 Evaluation of the micro receiver coil 91 5.4 Onboard energy storage 92 5.4.1 Fabrication of nano-biosupercapacitors 93 5.4.2 Electrochemical performance of “Swiss-roll” nBSC 97 5.4.3 Self-discharge performance and Bio enhancement: 98 5.4.4 Electrochemical and structural life time performance 100 5.4.5 Performance under physiologically conditions 101 5.4.6 Electrolyte temperature and flow dependent performance 102 5.4.7 Performance under hemodynamic conditions 105 5.4.8 Biocompatibility of nBSCs 105 5.5 Wireless powering and autarkic operation of SMARTS 108 5.5.1 Remote activation of an onboard IR-LED 108 5.5.2 Wireless locomotion of SMARTS 109 5.5.3 Effect of magnetic moment on SMARTS locomotion 111 5.5.4 Full 2D wireless locomotion control of SMARTS 112 5.5.5 Self-powered monolithic pH sensor system 114 5.6 Onboard remote actuation 119 5.6.1 Fabrication of integrable micro-arm 120 5.6.2 Remote actuation of integrable micro-arm 122 5.7 Flexibility of SMARTS 122 5.8 Onboard integrated electronics 123 5.9 Onboard organic electronics 124 5.9.1 Growth of BTBT-T6 as active semiconductor material 125 5.9.2 Confined Growth of BTBT-T6 to form Single-Crystal-Like Domain 128 5.9.3 Fabrication of OFET based on Single-Crystal-Like BTBT-T6 129 5.9.4 Carrier injection optimization 132 5.9.5 Performance of single-crystal-like BTBT-T6-OFET 133 5.10 Onboard flexible metal oxide electronics 136 5.10.1 Fabrication flexible ZnO TFT 138 5.10.2 Performance of ZnO TFT 139 5.10.3 Flexible integrated circuits 140 5.10.4 Logic gates 140 Chapter 6. Summary 142 Chapter 7. Conclusion and outlook 144 References 147 List of Figures & tables 173 Versicherung 177 Acknowledgement 178 Research achievements 180 Research highlight 183 Cover pages 184 Theses 188 Curriculum-vitae 191

Wir untersuchen minimale Suchstrategien für aktive Teilchen. Diese haben die Aufgabe, die Teilchen mit geringem Aufwand bezüglich Speicher- sowie Rechenkapazität möglichst effizient an ein Ziel zu bringen. Es wurden bereits zwei minimale Suchstrategien entwickelt, für die sich zeigen ließ, dass die Teilchen durch sie bei der Suche deutlich erfolgreicher sind als wenn sie einfachen Bewegungsmustern, wie der rein ballistischen oder der rein diffusiven Su- che, folgen, falls sie ihren Abstand zum Ziel zu jeder Zeit exakt kennen. Wir entwickeln ein mathematisches Modell, welches es möglich macht, beide Suchstrategien unter der realistischeren Bedingung zu untersuchen, dass die suchenden Teilchen den Abstand zum Ziel erst über die Messung der Konzentration von Signalmolekülen bestimmen müssen. Hierbei liegt ein besonderes Augenmerk auf dem molekularen Schrotrauschen, welches bei niedrigen Konzentrationen die Konzentrationsmessungen und damit auch die Abstandsmessungen beeinträchtigt. Wir zeigen, dass sich die stochastische Natur des Messprozesses bei der ersten Suchstrategie positiv auf den Erfolg der Suche auswirkt, wenn zwei Bedingungen erfüllt sind. Zum Einen muss den Messungen der Vergangenheit ein hohes Gewicht in der Bestimmung des momentanen Abstandes gegeben werden und zum Anderen dürfen die Messungen nicht stark verrauscht sein. Bei hohen Rauschstärken nimmt der Sucherfolg der ersten Suchstrategie stark ab, er ist jedoch noch ähnlich hoch, wie im idealisierten Fall, wenn die Teilchen den Abstand zum Ziel immer exakt kennen. Der Sucherfolg ist zudem auch dann noch um ein Vielfaches höher als der Sucherfolg bei einfachen Bewegungsmustern. Damit zeigt sich die erste Suchstrategie als stabil gegenüber dem molekularen Schrotrauschen. Für die zweite Suchstrategie stellen wir die begründete Vermutung auf, dass sie für hohe Rauschstärken effizienter funktioniert als für niedrige Rauschstärken. Außerdem gehen wir davon aus, dass die Suchstrategie bei niedrigen Rauschstärken deutlich ineffizienter ist als im idealisierten Fall, wenn die Teilchen den Abstand zum Ziel immer exakt kennen.:Inhaltsverzeichnis 1 Einleitung 1 2 Grundlegende Theorie zu einfachen Suchstrategien 7 2.1 Bewegung aktiver brownscher Teilchen 7 2.2 Zwei minimale Suchstrategien 9 2.3 Erfolgswahrscheinlichkeit für innere Suche bei erster Suchstrategie 12 2.3.1 Fall mit Rotationsdiffusion 12 2.3.2 Fall ohne Rotationsdiffusion 13 3 Zusammengesetzte Suchstrategien bei verrauschter Konzentrationsmessung 15 3.1 Radiale Konzentrationsverteilung der Signalmoleküle 15 3.2 Mathematisches Modell für die Detektion von Signalmolekülen 15 3.3 Informationsverarbeitung mittels Tiefpassfilter erster Ordnung 19 3.4 Unverrauschte Messung 20 3.4.1 Berechnung der Distanz bei Bewegung direkt auf Ziel 21 3.4.2 Berechnung der Distanz für allgemeine Winkel 22 3.5 Verrauschte Messung 24 3.6 Auswirkung der Konzentrationsmessung auf die Erfolgswahrscheinlichkeit der inneren Suche 25 3.7 NumerischeMethoden 28 4 Erfolgswahrscheinlichkeit der zusammengesetzten Suchstrategien 31 4.1 Einfluss der Integrationszeit des Tiefpassfilters auf das Umschaltverhalten der Agenten 31 4.2 Einfluss der Rauschstärke auf das Umschaltverhalten der Agenten 35 4.3 Erfolgswahrscheinlichkeit der ersten Suchstrategie 38 4.3.1 Bestimmung der optimalen Integrationszeit des Tiefpassfilters erster Ordnung 38 4.3.2 Erfolgswahrscheinlichkeit bei der inneren Suche in Abhängigkeit von der Rauschstärke 44 4.3.3 Optimaler Umschaltabstand für den Start der inneren Suche 46 4.4 Ausblick auf die zweite Suchstrategie 48 5 Zusammenfassung und Ausblick 53 Anhang 57 A Erfolgswahrscheinlichkeit bei der inneren Suche ohne Rotationsdiffusion 57 B Radiale Konzentrationsverteilung der Signalmoleküle 57 C Lösung des Tiefpassfilter erster Ordnung für die rauschfreie Messung 58 D Berechnung der Distanz bei rauschfreier Messung für Bewegung direkt auf Ziel 59 E Berechnung der Distanz bei rauschfreier Messung für allgemeine Winkel 60 Symbolverzeichnis 63 Literaturverzeichnis 65 / We investigate minimal search strategies for active particles. The task of these strategies is to bring the particles to a target as efficiently as possible with minimal memory and computing capacities. Two minimal search strategies have already been developed, for which it could be shown that the particles are significantly more successful in their search than when they follow simple motion patterns, such as the purely ballistic or the purely diffusive search, if they know their distance to the target exactly at all times. We develop a mathematical model that makes it possible to study both search strategies under the more realistic condition that the searching particles must first determine the distance to the target by measuring the concentration of signaling molecules. Here, we pay particular attention to the molecular shot noise, which at low concentrations affects the concentration measurements and thus also the distance measurements. We show that the stochastic nature of the measurement process has a positive effect on the success of the search in the first search strategy if two conditions are met. First, the past measurements must be given a high weight in determining the current distance and second, the level of molecular shot noise must be low. At high noise levels, the search success of the first search strategy decreases strongly, but it is still similar to the idealistic case, in which the particles always know the distance to the target exactly. Moreover, the search success is still many times higher than the search success of particles that use simple motion patterns. Thus, the first search strategy is shown to be stable against the molecular shot noise. For the second search strategy, we make the reasonable assumption that it works more efficiently for high noise levels than for low noise levels. We also assume that the search strategy is significantly more inefficient for low noise levels than in the idealistic case, in which the particles always know the distance to the target exactly.:Inhaltsverzeichnis 1 Einleitung 1 2 Grundlegende Theorie zu einfachen Suchstrategien 7 2.1 Bewegung aktiver brownscher Teilchen 7 2.2 Zwei minimale Suchstrategien 9 2.3 Erfolgswahrscheinlichkeit für innere Suche bei erster Suchstrategie 12 2.3.1 Fall mit Rotationsdiffusion 12 2.3.2 Fall ohne Rotationsdiffusion 13 3 Zusammengesetzte Suchstrategien bei verrauschter Konzentrationsmessung 15 3.1 Radiale Konzentrationsverteilung der Signalmoleküle 15 3.2 Mathematisches Modell für die Detektion von Signalmolekülen 15 3.3 Informationsverarbeitung mittels Tiefpassfilter erster Ordnung 19 3.4 Unverrauschte Messung 20 3.4.1 Berechnung der Distanz bei Bewegung direkt auf Ziel 21 3.4.2 Berechnung der Distanz für allgemeine Winkel 22 3.5 Verrauschte Messung 24 3.6 Auswirkung der Konzentrationsmessung auf die Erfolgswahrscheinlichkeit der inneren Suche 25 3.7 NumerischeMethoden 28 4 Erfolgswahrscheinlichkeit der zusammengesetzten Suchstrategien 31 4.1 Einfluss der Integrationszeit des Tiefpassfilters auf das Umschaltverhalten der Agenten 31 4.2 Einfluss der Rauschstärke auf das Umschaltverhalten der Agenten 35 4.3 Erfolgswahrscheinlichkeit der ersten Suchstrategie 38 4.3.1 Bestimmung der optimalen Integrationszeit des Tiefpassfilters erster Ordnung 38 4.3.2 Erfolgswahrscheinlichkeit bei der inneren Suche in Abhängigkeit von der Rauschstärke 44 4.3.3 Optimaler Umschaltabstand für den Start der inneren Suche 46 4.4 Ausblick auf die zweite Suchstrategie 48 5 Zusammenfassung und Ausblick 53 Anhang 57 A Erfolgswahrscheinlichkeit bei der inneren Suche ohne Rotationsdiffusion 57 B Radiale Konzentrationsverteilung der Signalmoleküle 57 C Lösung des Tiefpassfilter erster Ordnung für die rauschfreie Messung 58 D Berechnung der Distanz bei rauschfreier Messung für Bewegung direkt auf Ziel 59 E Berechnung der Distanz bei rauschfreier Messung für allgemeine Winkel 60 Symbolverzeichnis 63 Literaturverzeichnis 65

The next generation of biomedical tools requires reshapeable electronics to closely interface with biological tissues. This will offer unique mechanical properties and the ability to conform to irregular geometries while being robust and lightweight. Such devices can be achieved with soft materials and thin-film structures that are able to reshape on demand. However, reshaping at the submillimeter scale remains a challenging task. Herein, shape-controlled microscale devices are demonstrated that integrate electronic sensors and electroactive polymer actuators. The fast and biocompatible actuators are capable of actively reshaping the device into flat or curved geometries. The curvature and position of the devices are monitored with strain or magnetic sensors. The sensor signals are used in a closed feedback loop to control the actuators. The devices are wafer-scale microfabricated resulting in multiple functional units capable of grasping, holding, and releasing biological tissues, as demonstrated with a neuronal bundle.

Micro-electro-mechanical systems (MEMS) technology has had an increasing impact on industry and our society. A wide range of MEMS devices are used in every aspects of our life, from microaccelerators and microgyroscopes to microscale drug-delivery systems. The increasing complexity of microsystems demands diverse microfabrication methods and actuation strategies to realize. Currently, it is challenging for existing microfabrication methods—particularly 3D microfabrication methods—to integrate multiple materials into the same component. This is a particular challenge for some applications, such as microrobotics and microfluidics, where integration of magnetically-responsive materials would be beneficial, because it enables contact-free actuation. In addition, most existing microfabrication methods can only fabricate flat, layered geometries; the few that can fabricate real 3D microstructures are not cost efficient and cannot realize mass production. This dissertation explores two solutions to these microfabrication problems: first, a method for integrating magnetically responsive regions into microstructures using photolithography, and second, a method for creating three-dimensional freestanding microstructures using a modified micromolding technique. The first method is a facile method of producing inexpensive freestanding photopatternable polymer micromagnets composed NdFeB microparticles dispersed in SU-8 photoresist. The microfabrication process is capable of fabricating polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio. This method was used to demonstrate the creation of freestanding microrobots with an encapsulated magnetic core. A magnetic control system was developed and the magnetic microrobots were moved along a desired path at an average speed of 1.7 mm/s in a fluid environment under the presence of external magnetic field. A microfabrication process using aligned mask micromolding and soft lithography was also developed for creating freestanding microstructures with true 3D geometry. Characterization of this method and resolution limits were demonstrated. The combination of these two microfabrication methods has great potential for integrating several material types into one microstructure for a variety of applications.

This thesis seeks to advance the field of microrobotics by leveraging Bayesian principles and computational tools to design system parameters for information gain and microrobot propulsion. Inspired by living cells, the development of mobile robots on the micron scale (microrobots) promises new capabilities for advancing human health, renewable energy, and environmental sustainability. To help pave the way towards this goal we develop practical recipes for applying computational and analytical tools to physics-based dynamical models of our microrobot experiments. We apply methods of criticism and validation to identify robust models for the motion of magnetic particles at curved interfaces, and identify optimal conditions for propulsion in our model system. We then develop tools for identifying optimal experimental conditions for most efficiently learning model parameters. By studying microscale actuation in depth, we seek to provide a roadmap of how to apply these computational tools to other microrobot design challenges, accelerating the scientific process. In Chapter 1, we focus on the actuation of magnetic particles adsorbed at curved liquid interfaces by external fields, a phenomenon that can be utilized for applications such as droplet mixing or propulsion. To optimize these behaviors, the development and validation of predictive models are essential. We employ Bayesian data analysis as a principled approach to infer model parameters from experimental observations, assess the capabilities of candidate models, and select the most plausible among them. Specifically, we identify and validate a dynamical model which accounts for the effects of gravity and tilting of the particle, a Janus sphere, at the interface. We show how this favored model can predict complex particle trajectories with micron-level accuracy across the range of driving fields considered. Chapter 2 builds on this modeling to develop the optimal properties of a mobile liquid droplet, driven by an adsorbed magnetic particle. This configuration enables the design of responsive emulsions, which can be actuated by a magnetic field. This work develops the properties of such a swimmer and validates our findings with an experimental realization of a ferromagnetic ellipsoid adsorbed onto a stationary water droplet in decane. Accounting for geometric differences, the model developed in the previous chapter is demonstrated to be accurate for this new system. We find that the configuration of the magnetic moment of our ellipsoid prohibits swimming of the assembly, but if it can be modified during fabrication, propulsion is possible. In Chapter 3 we show how automated experiments based on Bayesian inference and design can accurately and efficiently characterize another microscale propulsion system, the acoustic field within resonant chambers used to propel acoustic nanomotors. Repeated cycles of observation, inference, and design are guided by a physical model that describes the rate at which levitating particles approach the nodal plane. We show how this iterative process serves to discriminate between competing hypotheses and efficiently converges to accurate parameter estimates using only a few automated experiments. This work demonstrates how Bayesian methods can learn the parameters of nonlinear hierarchical models used to describe video microscopy data of active colloids. Finally, the forward-looking perspective in Chapter 4 illustrates how best to leverage these techniques and models to provide a path forward for self-guided microrobots. Existing microrobots based on field-driven particles rely on knowledge of the particle position and the target destination to control particle motion through fluid environments. These external control strategies are challenged by limited information and global actuation, where a common field directs multiple robots with unknown positions. We discuss how time-varying magnetic fields can be used to encode self-guided behaviors of magnetic particles conditioned on local environmental cues. Programming these behaviors is framed as a design problem: we seek to identify the design variables (e.g. particle shape, magnetization, elasticity, stimuli-response) that achieve the desired performance in a given environment. We discuss strategies for accelerating the design process using the methods developed in this thesis—including automated experiments, computational models, and statistical inference—as well as other approaches such as machine learning. Based on the current understanding of field-driven particle dynamics and existing capabilities for particle fabrication and actuation, we argue that self-guided microrobots with potentially transformative capabilities are close at hand. This research offers a unique contribution by demonstrating the practicality and efficiency of Bayesian computational methods in microrobot design, and provides a template that is applicable anywhere that physics-based dynamical models can be used to guide experimental effort.

In the last decades, additive manufacturing (AM), also called three-dimensional (3D) printing, has advanced micro/nano-fabrication technologies, especially in applications like lightweight engineering, optics, energy, and biomedicine. Among these 3D printing technologies, two-photon polymerization (TPP) offers the highest resolution (even at the nanometric scale), reproducibility and the possibility to create monolithically 3D complex structures with a variety of materials (e.g. organic and inorganic, passive and active). Such active materials change their shape upon an applied stimulus or degrade over time at certain conditions making them dynamic and reconfigurable (also called 4D printing). This is particularly interesting in the field of medical microrobotics as complex functions such as gentle interactions with biological samples, adaptability when moving in small capillaries, controlled cargo-release profiles, and protection of the encapsulated cargoes, are required. Here we review the physics, chemistry and engineering principles of TPP, with some innovations that include the use of micromolding and microfluidics, and explain how this fabrication schemes provide the microrobots with additional features and application opportunities. The possibility to create microrobots using smart materials, nano- and biomaterials, for in situ chemical reactions, biofunctionalization, or imaging is also put into perspective. We categorize the microrobots based on their motility mechanisms, function, and architecture, and finally discuss the future directions of this field of research.